The present invention concerns a process for the preparation of a rhenium-based catalyst and the use thereof for the metathesis of olefins.
The metathesis of olefins, or a reaction for the mutual redistribution of the alkylidene groups, is of great practical interest, for example for mutual re-balancing of the light olefins which result from steam cracking such as ethylene, propylene and butenes.
Different types of catalysts can be used in the metathesis reaction, either homogeneous catalysts when the constituent elements thereof are all soluble in the medium of the reaction, or heterogeneous catalysts when at least one of the elements is insoluble in the reaction medium. The latter are particularly attractive when the active metal causes problems and it is necessary to envisage re-using same without losses. That is the case for example with rhenium-based catalysts.
There are not many rhenium-based supported catalysts which are active for the reaction for the metathesis of olefins. The oldest and most generally used is rhenium heptoxide deposited on inorganic oxides, in most cases alumina (British patent No. 1,954,864, British Petroleum Co Ltd, 1964), but also on supports comprising both alumina and another co-oxide (R Nakamura, Rec Trav Chim Pays-Bas, Vol 96, 1977, page M31). The use of organometallic co-catalysts such as tetraalkyltins associated with the catalyst comprising rhenium oxide on alumina permits, amongst other advantages, the metathesis of functional olefins (J C Mol, C Boelhouwer et al., J. Chem. Soc. Chem. Comm., 1977, page 198). W. Hermann claimed the use of complexes such as methyltrioxorhenium and pentamethylcyclopentadienyltrioxorhenium which are deposited on various inorganic oxides including in particular alumina and silica-aluminas (Hoechst, European patents 373,488-A and 522,067-A).